Hominins reached Asia at least 2.1 million years ago, researchers assert in an 11 July Nature paper. Stone tools they found in central China represent the earliest known evidence of humans or their ancient relatives living outside Africa.

Other scientists are convinced that the tools were made by hominins and are confident that they are as old as claimed. And although the tools’ makers are unknown, the discovery could force researchers to reconsider which hominin species first left Africa—and when. “This is a whole new palaeo ball game,” says William Jungers, a palaeoanthropologist at Stony Brook University, New York.

Most researchers say that hominins—the evolutionary line that includes humans—first left their African homeland around 1.85 million years ago. This is the age of the oldest hominin fossils discovered beyond Africa—from Dmanisi, Georgia, in the Caucasus region of Eurasia. The oldest hominin remains from East Asia, two incisors from southwest China, are around 1.7 million years old (see ‘Travelling Hominins’).

Archaeological finds made between 2004 and 2017 at a site called Shangchen in central China now challenge that orthodoxy. By studying and dating a sequence of ancient soils and deposits of wind-blown dust, a team of Chinese and British geologists and archaeologists led by Zhaoyu Zhu at the Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, has uncovered dozens of relatively simple stone tools. The youngest tools are 1.26 million years old, and the oldest date back to 2.12 million years.

The 2.12-million-year-old geological layers might not even represent the earliest hominin occupation of the region. John Kappelman, an anthropologist and geologist at the University of Texas at Austin and one of the paper’s referees, points out that the deepest—and so oldest—layers at the site are currently inaccessible because the region is actively farmed. Investigating them should be a priority, he says.

Polarity pattern

The deposits were dated using a method called palaeomagnetism, which uses well-documented flips in Earth’s magnetic field to date rock established between these events. The pattern of geomagnetic flips that occurred between 1.26 million and 2.12 million years ago is recorded in the magnetic minerals locked in the sediments at Shangchen.

Jan-Pieter Buylaert, a geologist at Aarhus University in Denmark who has worked on the sediments in this region of China, calls the dating “robust”.

Archaeologists are also confident that the tools are genuine. Study co-leader Robin Dennell, an archaeologist at the University of Exeter, UK, says his team has ruled out any natural processes, such as the churning of a river, that can make rocks look like tools. No ancient rivers are known at the Shangchen site, and the proposed tools are the only large stones present.

That absence of alternative explanations for the fractures seen on the stones is enough to persuade Zeljko Rezek, an archaeologist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. “The bottom line: I think these are truly stone tools,” he says.

Michael Petraglia, an archaeologist at the Max Planck Institute for the Science of Human History in Jena, Germany, and another of the paper’s reviewers, agrees that the tools are convincing. They are relatively simple, but this is a common feature of all stone tools from so early in the archaeological record, he says.

Hidden identity

The identity of their makers is, for now, unclear: no hominin bones have been recovered at Shangchen. “We would all love to find a hominin—preferably one with a tool in its hand,” says Dennell. Homo erectus is one possibility, because some of the earliest members of this species were found at Dmanisi. But Dennell thinks that the Shangchen toolmakers belonged to an earlier species in the genus Homo.

Petraglia and Rezek both say that the age of the tools—not to mention the possibility that hominins arrived in China even earlier than the 2.12-million-year mark—suggests that the toolmaker was a species such as Homo habilis. This relatively small-brained hominin is thought to have been confined to Africa between around 2.4 million to 1.4 million years ago.

Jungers holds open the possibility that the Shangchen toolmaker was a species of Australopithecus, a group of more ape-like hominins to which the iconic fossil Lucy belongs. So far, all Australopithecus fossils have been discovered in Africa.

The new finds imply that hominins covered vast distances before 2 million years ago—Shangchen is 14,000 kilometres from the nearest sites in East Africa where other hominins of this age have been found. It’s possible that the Shangchen toolmakers, hunter-gatherers, were simply following their foods, says Vivek Venkataraman, an evolutionary ecologist at Harvard University in Cambridge, Massachusetts.

The Shangchen finds are sure to encourage other researchers to hunt for further signs of hominins living in Eurasia before 2 million years ago, says Kappelman.

A few such claims for early Eurasian hominins have previously been made. In 2016, for instance, researchers presented evidence of 2.6-million-year-old stone tools at a site near the India–Pakistan border.

Dennell, who has worked in that region, is sympathetic to the idea of an early hominin presence there, but he says the evidence isn’t as clear-cut as his team’s finds in Shangchen. Proving a hominin presence at any archaeological site, he explains, requires establishing that the tools are real and that their geological context and dating are solid. “It does mean that you have to kiss an awful lot of frogs before you find a princess.”

This article is reproduced with permission and was first published on July 11, 2018.

Scientific American is part of Springer Nature, which owns or has commercial relations with thousands of scientific publications (many of them can be found at www.springernature.com/us). Scientific American maintains a strict policy of editorial independence in reporting developments in science to our readers.